Abstract : The control of blend morphologies during process is of prime importance in order to predict the final properties of polymer blends. A coextrusion technique combined with static mixers was developed in order to smartly blend polymeric melts and to optimize the blend morphologies during the flow in static mixers 1. The aim of this paper is to study the evolution of those blend morphologies during extrusion in a flat die. The effect of the viscosity ratio and the interfacial tension are also investigated. The experimental observations are confronted with numerical simulation results.